If it does not make any unusual noises then, most likely, the problem is a bad magnetron. If the microwave is less than 5 years old - the part should be under the limited manufacturer warranty and I would recommend to call Sears for service.

I have worked on several microwave with the same problem...no heat and it all point to the same components...
1. Check the diode
2. Check capacitor
3. Check magnetron
We hope it's the diode cause that's the cheapest part, magnetron varies from $140 -$160.

i have similar problem with KitchenAid microwave KEMC308SS04.
Question on transformer secondary testing... it shows 70 to 80 ohms between white and Chesis. Repair manual claims it should be 0. However read 70+ ohm at few places include one of the forum here. Appreciate advice.

Wanted to let others know, hoping it will help others.
In my case it turnout to be Diode.
When i tested diode using 9 v battery/multimeter, it tested correctly however, only odd thing was that black paint like coating was on leads so i changed diode even though it tested good under low voltage (using 9v battery) ... and sure enough microwave started working fine.
BTW, rest of the component testing procedures defined in service manual for magnetron. door switches, high voltage transformer did matched correctly except hi- voltage winding to the ground should be 50-80ohms not 0 ohm as stated in kitchenaid repair/service manual.

Hope this helps others.

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